Internal material, not testimonials: the proprietary procedures and schedule libraries themselves, training records showing what is taught in-house and how long it takes, project histories where his knowledge changed the outcome, and a supervisor's letter describing the knowledge concretely rather than praising the person.
Show the thing itself, then explain it
Petitions in this category are often thin because everything persuasive feels confidential. Redaction is preferable to omission. Provide the table of contents of the internal manual, sample pages of the schedule library with commercially sensitive values obscured, the calibration procedure written for the group's own sensors, and the internal defect taxonomy.
Add the training curriculum given to new technicians, with its duration, and any record of how long previous hires took to become independent. Include specific episodes: a batch that was saved, a controller fault diagnosed from behaviour rather than from a manual, a schedule developed for a species the standard tables handle badly. Finish with a letter from the person who supervises Tobias that describes what he knows and how he came to know it inside this organisation.
Avoid adjectives; they are the least persuasive part of any such letter.